1. Field of the Invention
The present invention relates to an apparatus and a method for controlling brake vacuum pressure, and more particularly, to an apparatus and a method for controlling brake vacuum pressure to supplement brake vacuum pressure that becomes insufficient by stopping operation of an engine to implement ISG.
2. Description of Related Art
A technology about an idle stop and go (ISG) system for improving fuel efficiency has been under focus with the increase in concern about the fuel efficiency of vehicles.
A technology for reducing fuel consumption in an idle operation state of an engine by stopping the operation of the engine in the idle operation state in accordance with ISG conditions when a vehicle stops has been proposed, in an ISG system of the related art. The ISG conditions include the information on a battery system, the engine, the information on a transmission system, and the information on a request for implementing ISG by a driver etc.
The operation of the ISG system is as follows.
Referring to FIG. 1, when a vehicle stops, an engine control unit (ECU) 12 determines whether to implement ISG by checking a signal of various ISG-related variables (14) and a brake vacuum pressure signal transmitted from a brake vacuum pressure sensor 13 and reduces fuel consumption by stopping the operation of an engine 11 in an idle operation state in accordance with the conditions after implementing the ISG. The ISG conditions include engine 11, the information on a battery system (not shown), a transmission system (not shown), brake vacuum pressure transmitted from a brake vacuum pressure sensor 13, and the information on the user's intention of control etc.
However, when the operation of engine 11 stops, a brake is operated by the operation of a brake booster and a master cylinder which use the vacuum pressure of engine 11, such that there is a problem that it is not possible to increase again the vacuum pressure even if the vacuum pressure reduces after engine 11 stops. That is, as the brake vacuum pressure cannot be increased again, the vehicle cannot implement ISG.
Meanwhile, as shown in FIG. 2, when it is determined whether the vacuum pressure of the brake decreases under a predetermined reference range after the ISG is implemented (S10), the ISG is maintained (S20) when the vacuum pressure does not decrease under the predetermined reference range, but the engine is forced to restart when the vacuum pressure decreases under the predetermined reference range.
As described above, in the related art, since a vehicle is forced to restart for safety when vacuum pressure decreases under a predetermined reference range by continuous operation of a brake pedal under unexpected circumstances after the vehicle stops or implements ISG, the time for keeping the ISG to improve fuel efficiency reduces and reliability of the system is deteriorated by the forcible restart.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.